1. Technical Field
The present invention relates to an engine starting apparatus capable of starting an engine at a high rotational speed.
2. Related Art
Conventionally, a starter for starting an engine is provided with a speed reducer in order to generate a torque equal to or greater than a pass-over torque at high temperatures where the engine load can be excessive. For example, a starter, as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-257482, is provided with a planetary reducer between an armature axis and an output shaft of a motor, thereby reducing a motor speed, that is, amplifying the motor torque, and transmitting the torque to the output shaft. Such a starter is referred to as a speed-reduction starter.
However, it is inevitably difficult for such a speed-reduction starter to increase a cranking speed, which may cause a relative speed between the engine speed and the motor speed. In the presence of such a relative speed, a tooth surface of a pinion may strike a tooth surface of a ring gear during a compression stroke of the engine, which may cause excessive impact between the pinion and the ring gear. Thus, the speed-reduction starter may suffer from noise caused by stress and impact on a driver of the starter. Particularly, when the engine is in a warmed-up state, engine acceleration during an expansion stroke is increased, which inevitably leads to an increased relative speed between the high engine speed and the motor speed. The impact during the compression stroke is increased with increasing relative speed between the high engine speed and the motor speed.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a starter capable of preventing an impact on the starter from occurring during a compression stroke at starting of the engine.